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DCO Dicotyledons --- Dicotyledonae --- Gossypium raimondii --- Malvaceae --- agriculture --- genetic improvement

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Gossypium hirsutum --- Gossypium raimondii --- Introgression --- Interspecific hybridization --- Gossypol --- irradiation. --- irradiation --- Induced mutation --- Gossypium sturtianum

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The objective of this work is to introgress into the main cultivated species of cotton, Gossypium hirsutum L., a reduced level of gossypol in the seeds for food and feed uses, and a high level of gossypol in the remaining organs to limit pest incidence. Two trispecies hybrids designated TSH for G. thurberi x G. sturtianum x G. hirsutum, and HRS G. hirsutum x G. raimondii x G. sturtianum were created. Both trispecies hybrids have 52 chromosomes and present a reduced pollen fertility, with 2.90 % in TSH and 8.97 % in HRS. Recurrent backcrossing to G. hirsutum as pollinator and selfing of some progenies resulted in seeds which were rescued by in vitro culture. The gossypol gland morphogenesis was repressed totally or partially in the seeds of the plants obtained. The genetic control of this repressive mechanism is discussed. Cytogenetic analyses of the trispecies hybrids and their progenies showed a relatively high level of chromosome pairing and chiasmata, suggesting a high level of intergenomic exchanges. The high pollen fertility (80 %) observed in the third generation of backcross progenies should allow the utilization of suitable crossing schemes which can break undesirable linkages and enhance exchanges. Analyses of genetic distances using RAPD (random amplified polymorphic DNA) and AFLP (amplified fragment length polymorphism) allowed the identification of progenies sharing the highest genetic similarity with G. hirsutum. The use of RFLP (restriction fragment length polymorphism) probes specific to cotton chromosomes evidenced the introgression of specific segments of chromosomes from the wild parental species. The type of introgression revealed by these RFLP probes are discussed, and crossing schemes to enhance recombinations are proposed. Plants developed in this study constitute a valuable germplasm for the introgression of useful agronomic traits from the wild parental species into G. hirsutum.

Gossypium hirsutum --- Gossypium --- Hybrids --- Alkaloids --- Biosynthesis --- Morphogenesis --- cytogenetics --- Genetic polymorphism --- Gossypium raimondii --- Gossypol --- Gossypium thurberi --- Gossypium sturtianum